#include <iostream>
using namespace std;

int climbStairs(int n);

int main(int argc, char **argv){

    cout<<climbStairs(35)<<endl;

    return 0;
}

int climbStairs(int n) {
    // Start typing your C/C++ solution below
    // DO NOT write int main() function
    int prepre = 1;
    int pre = 1;
    for(int i=2; i<=n; ++i){
        int cur = pre + prepre;
        prepre = pre;
        pre = cur;
    }
    return pre;
}